Many telecommunication systems comprises base band units (or BBUs), also named remote equipment controllers (or RECs) in the CPRI (Common Public Radio Interface) terminology, that are coupled to remote radio-heads (or RRHs), also named remote equipments (or REs) in the CPRI terminology, via a (digital) transport network. Digitised base band complex in-phase (I) and quadrature phase (Q) samples defining data are transported over this transport network.
More precisely, these IQ samples are into (AxC) containers of digital data frames, for instance of the CPRI type and generated by the remote equipment controllers and the remote equipments. These digital data frames are processed before being integrated into transport frames that a transport network is able to transport. This process usually consists in a bandwidth requirement optimisation and a rate adaptation between the IQ sampling rate and the transport network rate. For instance, in case where the transport network is an optical transport network (or OTN), the CPRI digital data frames are encapsulated into transport frames named optical transport units (or OTUs).
The OTN may be, for example, a Passive Optical Network (PON), for example a 10 Gigabit Passive Optical Network (10GPON), a Wave Division Multiplex Passive Optical Network (WDM PON), a WDM overlay to a 10GPON, a CDWM optical ring, or a DWDM optical ring.
In an optical transport network, optical fibres can be used as point-to-point links between remote radio-heads and base band units. Typically, when a base band unit controls N remote radio-heads, there may be N optical fibres coupling this base band unit to these remote radio-heads.
As it is not always possible to daisy-chain the remote radio-heads and to share the physical links used, more and more dedicated links are required and the available bandwidth is not used efficiently.
Moreover, the CPRI bit stream is carried as a constant bit rate stream, and there is no solution that optimizes either the line coding and/or the bandwidth required to carry the payloads of the CPRI digital data frames and that enables aggregation and multiplexing of CPRI links.